More stringent engine emission standards regulated by the Environmental Protection Agency (EPA) provide incentive to study and to apply advanced combustion modes in internal combustion engines. Among recently proposed advanced combustion modes, the Homogeneous Charge Compression Ignition (HCCI) engine stands out as a very promising technology with better fuel economy and lower pollutant emissions compared to conventional diesel and gasoline engines. HCCI utilize a pre-mixed homogeneous charge of air/fuel, which is auto-ignited by engine compression and burns quickly to maximize combustion efficiency. As a result, the fuel chemistry plays a dominant role in combustion phasing and engine performance.
One of the major hurdles to creating commercially viable HCCI engines is developing technology to extend the engine high load limit. Because the chemical kinetics control combustion, the chemical properties of fuel components play a dominant role in HCCI engine performance. Combustion stability can also be a problem for HCCI engines under low load condition due to large cycle variations, i.e., during engine idling. This requires a fuel that has slow burning rate under high load but is still reactive under low load condition for HCCI engines. Accordingly, a need exists for improved hydrocarbon fuels that provide increased power and a broader operating range in HCCI engines, including increased load limit.